Make sure all functions used in libsandbox.c is declared static. Define
SB_STATIC in localdecls.h for this. Include sandbox_futils.c rather than
linking with its object. Hopefully this will fix bug #90153.

Fix inverse test logic in canonicalize.c, use a strncpy. Fix gcc warning in
getcwd.c. Add symbols.in and logic to Makefile.am to generate symbol versions
for glibc and other libc's that use this. Update libsandbox.c to use these
symbol versions if available. Fix exec wrapper to re-export LD_PRELOAD if the
process unset it.